1. Field of the Invention
The present invention relates to a reversing cold rolling apparatus for manufacturing stainless steel sheets, silicon steel sheets, etc., using a reversing cold rolling mill.
2. Description of the Related Art
When materials that are highly resistant to deformation such as stainless steel sheets or silicon steel sheets are cold rolled, reversing rolling is generally carried out thereon by using a small-roller rolling mill such as Sendzimir Mill. That is, as shown in FIG. 1B, a steel strip 14 is repeatedly rolled to be formed into a predetermined thickness while being uncoiled and coiled several times between a pair of coiling-uncoiling units 11 and 12.
However, during the uncoiling of a steel strip, since several number of turns of the coiled steel strip 14, in a longitudinal end portion (referred to as an end portion below), are always needed to be left on mandrels of the coiling-uncoiling units 11 and 12 for maintaining proper strip tension, unrolled portions coiled all the way, are produced that is a faulty portion called "an unrolled portion" by adding thereto a partial length of a steel strip 14 corresponding to the path between the coiling-uncoiling unit and the place directly below operating rollers.
Accordingly, in order to minimize this faulty portion, a coil preparatory line, a pre-rolling process, is conventionally arranged separately, in which dummy strips known as "leader strips" are welded to both ends of a steel strip or ends of steel strips are welded to be connected to each other directly or via a dummy strip to increase the steel strip length. This is done so that the faulty portion is reduced, which leads to improvements in yield, etc.
The coil preparatory line may also often includes a side trimmer for cutting off strip edges that to remove faulty portions located in the lateral end portions (referred to as an edge portion below) of a steel strip or to adjust the lateral length of a steel strip.
Structural examples of the above-mentioned coil preparatory line and a rolling line will be now described. As shown in FIG. 1A, the coil preparatory line is formed of an uncoiling unit 1 for un-coiling steel strips 10, a rough leveler 2 for modifying roll sets of the steel strips 10, a shear 3 for cutting off end portions of the steel strips 10 for welding, a dummy strip supplying unit 4 for supplying dummy strips (not shown), a welder 5 for welding end portions of the steel strips 10 to each other or welding an end portion of the steel strip 10 to an end portion of the dummy strip, a grinder 6 for grinding welded portions so as to smooth the surfaces thereof, a side trimmer 7 for cutting off edge portions of the steel strip 10, masher rollers 8 for smoothing burrs in the cutting surfaces produced by the side trimmer 7, and a coiling unit 9 for coiling the steel strip 10.
A pair of deflector-pinch rollers 30 are also illustrated in the drawing.
The above-mentioned shear 3, the dummy strip supplying unit 4, the welder 5, and the grinder 6 form a joining unit according to the present invention. The grinder 6 is not an essential component of the joining unit. The side trimmer 7 and the masher rolls 8 are also not compulsory components of the joining unit.
As shown in FIG. 1B, the rolling line is formed of a coiling-uncoiling unit 11 in the inlet side, a rolling mill 13, and a coiling-uncoiling unit 12 in the outlet side. Deflector rollers 15 are also illustrated in the drawing.
However, since the coil preparatory line and the cold rolling line have been conventionally independent of each other, the following problems as described below in items (1) to (4) are involved.
(1) The coil preparatory line and the reversing cold rolling line are required to have respective workers assigned to them.
(2) These lines require handling operations that the steel strip completed with operating in the coil preparatory line is coiled, for a time, in the coiling unit located in the outlet side of the coil preparatory line to be transferred out of the line for tentative storing on a coil yard; then, one of the waiting steel strips on the coil yard is set on the coiling-uncoiling unit in the cold rolling line to be fed in the rolling line.
In addition, in the cold rolling line, that has a delivering unit disposed in the inlet side for reducing the down time (set-up time) of the line, the steel strips tentatively waiting on the coil yard, are set on the delivering unit.
(3) Since both the coil preparatory line and the reversing cold rolling line are independent of each other, ineffective processes such as coiling and delivering are repeated, and plural coils have to be treated in the coil preparatory line, in advance while waiting in a predetermined place so that the next coil can be fed to the rolling line just after a preceding coil is completed rolling.
(4) The steel strips are likely to be damaged during he handling operations.
In order to solve the above-mentioned problems, a single line may be proposed, in which the coil preparatory line and the reversing cold rolling line are simply united in series, i.e., after welding steel strips to each other or welding between a steel strip and a dummy strip, rolling can be successively performed. However, this line has the following problems.
(5) Since a steel strip has to be stopped during welding operations, rolling operations should be also stopped, resulting in reduced productivity in rolling operations.
(6) The distance from the uncoiling unit to the operating rollers is increased, therefore the length of the dummy strip is increased to that extent, requiring a larger-scale dummy strip supplying unit and increased cost in accordance with increased length of the dummy strip.
(7) Arranging plural rolling mills in series to replace reversing rolling with one-way rolling can be considered; however, the cost of equipment is increased.
Therefore, any single line, in which the coil preparatory line and the reversing cold rolling line are united, has not been built yet because of the reasons of items (1) to (7).